The oxidation reaction of ammonia, namely, nitrification caused by the action of soil micro-organisms results in the serious loss of nitrogen fertilizers used for agricultural and horticultural production, and the pollution of soil environment. In order to inhibit such soil nitrification, mainly such synthetic chemicals have so far been used as nitrapyrin (2-chloro-6-Trichloromethylpyridine) and dicyandiamide (See, for example, Patent Reference 1.).
Among the synthetic chemicals, nitrapyrin is so highly volatile that it shows almost no effect under the condition where the earth temperature is over 20° C., and hence it has only limited use in the limited environment such as winter crop in North America.
On the other hand, dicyandiamide is effective at higher temperature compared with nitrapyrin, but since its use concentration is high and price is high, it seriously affects the cost of agricultural production, thereby utilizable area is limited. From such background, the development of economical nitrification inhibition is sought which could be used in the wide area from tropical to temperate zone.
Non-Patent References 1 and 2 report the phenomenon in which nitrification is inhibited in the soil where a tropical pasture grass of rice family, creeping signal grass (Brachiaria humidicola), grows.    [Patent Reference 1] Japanese Laid-Open Patent Publication H11-278973A (1999)    [Non-Patent Reference 1] CIAT 1983 annual report, p. 224    [Non-Patent Reference 2] CIAT 1985 annual report, p. 210-211    [Non-Patent Reference 3] USFDA 21CFR 573,640    [Non-Patent Reference 4] Iizumi et al., Appl. Environment. Mcrobiol., vol. 64, p. 3656-3662, 1998